1. Field of the Invention:
The present invention relates to heating and cooling systems. More specifically, the present invention relates to methods and apparatus for heating the passenger compartment of a motorized vehicle.
While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility.
2. Description of the Related Art:
Conventional automotive passenger compartment heating systems utilize a heat exchanger to tap thermal energy from a coolant loop which serves ordinarily to cool the engine. While such systems have heretofore been somewhat adequate for this task, it has been recognized that as automotive engines become more and more efficient, waste heat from the engine may be insufficient to heat the passenger compartment to desired temperatures within nominal time constraints. Accordingly, a need has been recognized in the art for a fast acting, automotive passenger heating system which does not require heat from engine cooling system for effective operation.
One alternative approach involves the use of a separate system with a heat pipe and a blower. A heat pipe is a passive hermetically sealed closed container which contains a capillary-wick structure, retained against the inner walls of the pipe soaked by a small amount of vaporizable (working) fluid. The heat pipe employs a vaporization-condensation cycle with the capillary wick pumping the condensate to the evaporator. That is, when heat is applied to one end of the pipe, the working fluid vaporizes, travels to the cool end of the pipe and condenses. In the process of condensation, the fluid releases the heat to the exterior of the pipe. The working fluid returns to the warm portion of the pipe via the wick and the process is repeated. As the vapor pressure drop between the evaporator and condenser is very small, the cycle is essentially an isothermal process. With proper design, the heat pipe can transfer large amounts of heat with minimal temperature losses. See U.S. Pat. No. 4,007,777 entitled Switchable Heat Pipe Assembly by Tsu Hung Sun, issued Feb. 15, 1977.
Unfortunately, the heat pipe/blower system exhibits considerable thermal expansion necessitating the use of an expensive bellows and additional hardware. This system also requires an air cooled heat exchanger.
Another system developed by Volvo and described in U.S. Pat. No. 4,693,306 utilizes a heat pipe between the cooling system and the exhaust pipe of the vehicle. However, no control system is disclosed for this system. Accordingly, there is a need in the art for a thermally controllable heat pipe based passenger compartment heating system utilizing exhaust heat from the vehicle.